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//
// Zig has builtins for mathematical operations such as...
//
// @sqrt @sin @cos
// @exp @log @floor
//
// ...and lots of type casting operations such as...
//
// @as @intToError @intToFloat
// @intToPtr @ptrToInt @enumToInt
//
// Spending part of a rainy day skimming through the complete
// list of builtins in the official Zig documentation wouldn't be
// a bad use of your time. There are some seriously cool features
// in there. Check out @call, @compileLog, @embedFile, and @src!
//
// ...
//
// For now, we're going to complete our examination of builtins
// by exploring just THREE of Zig's MANY introspection abilities:
//
// 1. @This() type
//
// Returns the innermost struct, enum, or union that a function
// call is inside.
//
// 2. @typeInfo(comptime T: type) @import("std").builtin.TypeInfo
//
// Returns information about any type in a TypeInfo union which
// will contain different information depending on which type
// you're examining.
//
// 3. @TypeOf(...) type
//
// Returns the type common to all input parameters (each of which
// may be any expression). The type is resolved using the same
// "peer type resolution" process the compiler itself uses when
// inferring types.
//
// (Notice how the two functions which return types start with
// uppercase letters? This is a standard naming practice in Zig.)
//
const print = @import("std").debug.print;
const Narcissus = struct {
me: *Narcissus = undefined,
myself: *Narcissus = undefined,
echo: void = undefined, // Alas, poor Echo!
fn fetchTheMostBeautifulType() type {
return @This();
}
};
pub fn main() void {
var narcissus: Narcissus = Narcissus{};
// Oops! We cannot leave the 'me' and 'myself' fields
// undefined. Please set them here:
narcissus.me = &narcissus;
narcissus.??? = ???;
// This determines a "peer type" from three separate
// references (they just happen to all be the same object).
const Type1 = @TypeOf(narcissus, narcissus.me.*, narcissus.myself.*);
// Oh dear, we seem to have done something wrong when calling
// this function. We called it as a method, which would work
// if it had a self parameter. But it doesn't. (See above.)
//
// The fix for this is very subtle, but it makes a big
// difference!
const Type2 = narcissus.fetchTheMostBeautifulType();
// Now we print a pithy statement about Narcissus.
print("A {s} loves all {s}es. ", .{
maximumNarcissism(Type1),
maximumNarcissism(Type2),
});
// His final words as he was looking in
// those waters he habitually watched
// were these:
// "Alas, my beloved boy, in vain!"
// The place gave every word back in reply.
// He cried:
// "Farewell."
// And Echo called:
// "Farewell!"
//
// --Ovid, The Metamorphoses
// translated by Ian Johnston
print("He has room in his heart for:", .{});
// A StructFields array
const fields = @typeInfo(Narcissus).Struct.fields;
// 'fields' is a slice of StructFields. Here's the declaration:
//
// pub const StructField = struct {
// name: []const u8,
// field_type: type,
// default_value: anytype,
// is_comptime: bool,
// alignment: comptime_int,
// };
//
// Please complete these 'if' statements so that the field
// name will not be printed if the field is of type 'void'
// (which is a zero-bit type that takes up no space at all!):
if (fields[0].??? != void) {
print(" {s}", .{@typeInfo(Narcissus).Struct.fields[0].name});
}
if (fields[1].??? != void) {
print(" {s}", .{@typeInfo(Narcissus).Struct.fields[1].name});
}
if (fields[2].??? != void) {
print(" {s}", .{@typeInfo(Narcissus).Struct.fields[2].name});
}
// Yuck, look at all that repeated code above! I don't know
// about you, but it makes me itchy.
//
// Alas, we can't use a regular 'for' loop here because
// 'fields' can only be evaluated at compile time. It seems
// like we're overdue to learn about this "comptime" stuff,
// doesn't it? Don't worry, we'll get there.
print(".\n", .{});
}
// NOTE: This exercise did not originally include the function below.
// But a change after Zig 0.10.0 added the source file name to the
// type. "Narcissus" became "065_builtins2.Narcissus".
//
// To fix this, I've added this function to strip the filename from
// the front of the type name in the dumbest way possible. (It returns
// a slice of the type name starting at character 14 (assuming
// single-byte characters).
//
// We'll be seeing @typeName again in Exercise 070. For now, you can
// see that it takes a Type and returns a u8 "string".
fn maximumNarcissism(myType: anytype) []const u8 {
// Turn '065_builtins2.Narcissus' into 'Narcissus'
return @typeName(myType)[14..];
}
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